1. Field of the Invention
The present invention relates to a polymerizable composition and a lithographic printing plate precursor, and more specifically a polymerizable composition suitable for a photosensitive layer of a negative lithographic printing plate precursor that is capable of high-speed writing with a laser beam, and a negative lithographic printing plate precursor using the polymerizable composition.
2. Description of the Related Art
As lithographic printing plate precursors, PS plates comprising a hydrophilic support having provided thereon a lipophilic photosensitive resin layer have so far been widely used. As the plate-making methods, methods of obtaining desired printing plates by mask exposure (areal exposure) via a lith film and then dissolving and removing the non-image area are generally used.
Digitized techniques of electronically processing, accumulating and outputting image data using a computer have prevailed in recent years, and various image output systems corresponding to these digitized techniques have been put to practical use. As a result, a computer-to-plate (CTP) technique of directly making a printing plate by scanning digitized image data with high convergent light such as a laser beam without using a lith film is eagerly desired. With such a tendency, it has become an important technical subject to obtain a printing plate precursor adaptable to this purpose.
As such a lithographic printing plate precursor capable of scanning exposure, a constitution comprising a hydrophilic support having provided thereon a lipophilic photosensitive resin layer (hereinafter also referred to as “a photosensitive layer”) containing a photosensitive compound capable of generating an active seed such as a radical and a Brφnsted acid by laser exposure has so far been proposed and now on the market. A negative lithographic printing plate can be obtained by scanning exposing the lithographic printing plate precursor with laser beams on the basis of digital data to generate an active seed, causing physical or chemical changes on the photosensitive layer by the action of the active seed to make the photosensitive layer insoluble, and then development processing. In particular, a lithographic printing plate precursor comprising a hydrophilic support having thereon a photopolymerization type photosensitive layer containing a high speed photopolymerization initiator, an addition polymerizable ethylenic unsaturated compound, and a binder polymer soluble in an alkali developing solution, and, if necessary, an oxygen-shielding protective layer, is excellent in productivity and easy of development process, and has advantages that excellent in resolution and adhesion of inks, so that such a lithographic printing plate precursor is promising as a printing plate having preferred printing properties.
The disposal of waste solutions discharged with alkali development processing is a great interest of the industry at large in recent years from the consideration for the protection of global environment, and public attention is attracted to the measure of reducing the load of waste solution proposal by development process (e.g., mild development process with solutions having pH of from 4 to less than 10) without depending upon strong alkali developing solutions having pH 10 or more containing high concentration of alkali that is the main component of developing solutions (e.g., potassium hydroxide that is generally called a strong base).
Accordingly, it has been increasingly strongly desired to obtain a lithographic printing plate precursor exhibiting preferred printing properties in mild development process with solutions having pH of from 4 to less than 10, not to speak of strong alkali development process of pH 10 or more.
For the purpose of heightening the press life of a printing plate, alkali-soluble polyurethane resin binders (e.g., refer to JP-A-63-113450 (the term “JP-A” as used herein refers to an “unexamined published Japanese patent application”) and JP-B-7-120038 (the term “JP-B” as used herein refers to an “examined Japanese patent publication”)), and alkali-soluble acrylic resin binders having an ethylenic unsaturated bond at side chains (e.g., refer to JP-B-3-63740 and JP-A-10-10719) have conventionally been used.
In improving press life, it was general means to modify the copolymerization components of the polyurethane resin binder (e.g., refer to JP-A-11-352691 and JP-A-2001-125257), or modify the structure of the unit containing an ethylenic unsaturated bond in the acrylic resin binder (e.g., refer to JP-A-2002-229207).
However, in the examination of the improvement of press life in the polyurethane resin binder, the trade-off with aging developability (almost the same meaning as a raw preservation property) due to high aggregation ascribable to the urethane bonding in the polyurethane structure, or in the examination of the improvement of press life by the modification of the unit structure containing an ethylenic unsaturated bond at side chains in the acrylic resin binder, the trade-off with aging developability ascribable to dark polymerization of the double bond parts C═C of side chains is latently involved.
An excellent technique of getting rid of the trade-off of press life and a raw preservation property has been found in recent years (e.g., refer to JP-A-2004-109851). According to the technique, similarly to JP-A-2002-229207, since a specific alkali-soluble polymer has at the side chain an ethylenic unsaturated bond having high radical reactivity, a high density and tenacious crosslinking structure is rapidly formed in the polymer compound by the supply of energy at the time of exposure, so that high sensitivity and excellent press life can be realized.
Additionally, the specific alkali-soluble polymer in JP-A-2004-10985 1 is characterized in that it has hydrogen bonding groups and cyclic structures as the linking groups of the terminal ethylenic unsaturated groups with the main chain polymer and the copolymer component, and the hydrogen bonding property of such linking groups and the bulkiness of the cyclic structures inhibit the rotation around the polymer main chain and maintain a high glass transition temperature, as a result the dark polymerization by thermal motion of the terminal ethylenic unsaturated groups is prevented to reveal a good raw preservation property.
However, a technique capable of actually reconciling press life with a raw preservation property has not been found yet other than the technique (concept) of JP-A-2004-109851, so that a technique capable of reconciling press life with a raw preservation property looking steadily at not only alkali development process but also the non-alkali development process has been desired.